JP2001358786A - Method and device for deciding fsk signal frequency and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device which enable accurate frequency decision even at sampling with a frequency in which a sampling rate is low. SOLUTION: A storing means is provided which stores sampling values as one set before and after the time when the positive/negative of a sampling value of a sampled signal waveform or the magnitude relation to an offset value is inverted. The intersections where a straight line connecting a set of sampling values stored in the storing means crosses with the time base of a zero value or the offset value are calculated, the half period of a sampled signal is calculated on the basis of the part between the crosses intersections, and a frequency is calculated on the basis of the derived half period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for determining a frequency, and more particularly, to a frequency shift keying (Frequency Shift Keying) method.
ft Keying (referred to as “FSK”) signal frequency determination method and apparatus.

[0002]

2. Description of the Related Art Conventionally, an FSK signal is used as a digital modulation method because it is suitable for mobile communication and the like. As a method of determining the frequency of the FSK signal, a zero-crossing method, a digital filter method (such as a band-pass filter), an autocorrelation method, and the like are known.

[0003] Each of these methods is efficient when the sampling rate is high, but is not very effective when the sampling rate is low.

A pre-communication information notification service (number display service) is provided for those utilizing the FSK signal. This service uses an FSK signal as an information transmission signal.

[0005] In addition to domestic FS,
There is a similar service using the K signal.
D, Call Number Delivery ”(caller ID, caller number delivery) and the like. An analog modem for receiving this service by a general household analog terminal that receives a signal via a two-wire metallic line is also used.

FIG. 6 is a diagram schematically showing a system configuration of a wireless access network. In this radio access network system, a radio communication system is interposed between a telephone and an exchange, thereby shortening a section in which a 2-wire metallic wire (cable) is laid, thereby reducing costs. In FIG. 6, 101 is a fixed telephone, 102
Is a slave station (wireless access device) accommodating a plurality of fixed telephones 101, 103 is a base station (wireless access device) wirelessly connected to the plurality of slave stations 102, 104 is a time switch (TSW), 105 is an FSK signal Frequency judgment device, 1
Reference numeral 06 denotes an AD converter, and reference numeral 107 denotes an exchange. The base station 103 is connected to a time switch (Time Switch) 104 and has an AD (analog-digital) converter 106.
Is connected to a switch 107 via a two-wire telephone line (two-wire metallic line) 108, and an output (downstream signal) of an AD (analog-digital) converter 106 is input to the time switch 104. The base station 103 is connected to the time switch 104, and a frequency determination device 105 is connected via a digital highway 109.

[0007]

SUMMARY OF THE INVENTION For example, audio and the like are set to 8 kHz.
The digital signal sampled at z has a period of 125μ
sec (microseconds). A digital signal can be easily demodulated at a high sampling rate, but difficult to demodulate at a low sampling rate. To accurately demodulate a signal sampled at 8 kHz,
It is necessary to set the sampling rate to a certain level or more and perform demodulation. As a result, it is necessary to increase the processing capacity, which increases the cost.

In the case of demodulating an FSK signal, in the zero-cross method, a mark frequency and a space frequency are determined based on the number of samplings of the mark and the space determined based on a predetermined sampling frequency. Is going. For example, if the center frequency is 1500 Hz (period is 666.67 μsec), the mark frequency is 1530 Hz (period is 653.59 μsec), the space frequency is 1470 Hz (period is 680.27 μsec), and the sampling frequency is 64 KHz, the mark has a sampling frequency of about 41.9 Hz. The number of times and space is about 43.5 times, and the mark and space can be determined. However, in this case, if the sampling frequency is 16 KHz, the sampling period is 62.5 μsec, and the number of times of sampling is about 1
It becomes 0.5 times and the space becomes about 10.9 times, and it becomes impossible to judge the mark and the space. Therefore, the mark,
In order to determine the space, it is necessary to set the sampling frequency to a certain level or more.

Further, the FSK signal is transmitted to the A / D converter 10
6, when the signal is transmitted through a time-division time slot by the time switch 104 and the sampling frequency is low, when the frequency of the signal waveform is determined by the frequency determination circuit 105 or the like, the signal waveform changes. Since there are few points, the frequency may be erroneously detected.

Therefore, there is a need for a frequency determination method for accurately and quickly determining.

For example, Japanese Patent Application Laid-Open No. 9-233137 discloses an FSK demodulator that accurately determines a mark or a space at a low sampling frequency and reduces distortion by setting the time between zero-cross points based on the value of a sampling point. An FSK demodulation device having a calculating means, wherein a sampling point section in which the sign of a sampling value changes from negative to positive or from positive to negative is stored as a section where a zero crossing point exists on a time axis. An intersection calculating means for calculating an intersection of a line connecting the sampling points at both ends between the sampling points stored in the storage means and the time axis; and an intersection position calculated by the intersection calculating means as a zero-cross point. There has been proposed a configuration of an FSK demodulator having a time calculating means for calculating a time from a sampling point.

Further, as a frequency determination device, Japanese Patent Laid-Open No. 9-1
No. 66630 discloses that an input signal is sampled at a fixed period, converted into digital data, the timing of each zero-cross point is obtained based on data at a plurality of points sandwiching the zero-cross point, and the time between adjacent zero-cross points is input. There has been proposed a frequency measuring apparatus which detects a signal as one cycle of a fundamental cycle of the signal and obtains the frequency of the input signal from the signal. As will be apparent from the following description, the present invention provides an apparatus and a method for further speeding up the period determination.

Accordingly, the present invention has been made in view of the above problems, and a main object of the present invention is to enable accurate frequency determination even when sampling is performed at a low sampling rate. An object of the present invention is to provide a method and an apparatus, and a recording medium.

[0014]

According to the present invention to achieve the above object, the present invention stores a set of sampling values before and after a sign value of a sampled signal waveform, or before and after the magnitude relationship with an offset value is inverted. Storage means for performing
An intersection calculating means for finding an intersection at which a straight line connecting a set of sampling values stored in the storage means and a time axis of a zero value or an offset value intersects, based on an intersection obtained by the intersection calculating means. There is provided a cycle calculating means for calculating a half cycle of the sampled signal, and a frequency calculating means for calculating a frequency based on the half cycle derived by the half cycle calculating means.

According to the present invention, when a signal waveform which is determined based on a high frequency and a low frequency is included, a half cycle calculating means for calculating a half cycle time of each of the high frequency and the low frequency, and the half cycle calculating means obtains the half cycle time. A determination reference time calculating means for obtaining a time as a determination reference based on the obtained half cycle; and a comparison determination means for performing a comparison determination based on the time obtained by the determination reference time calculation means.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus according to an embodiment of the present invention will be described. The present invention includes a sampling device 1, a memory 2, a calculation device 3, and a determination device 4.

The sampling device 1 samples an input signal and stores the result in the memory 2.

The arithmetic unit 3 calculates an intersection based on the data stored in the memory 2, obtains a period based on the intersection, and obtains a frequency from the obtained period.

The determination device 4 calculates a half cycle and calculates a determination reference time. Perform frequency comparison judgment.

In one embodiment of the present invention, the frequency of the FSK signal is calculated by the following configuration.

FIG. 2 is a diagram showing an example of the configuration of the frequency determination device 10 according to one embodiment of the present invention. This frequency determination device 10 includes the arithmetic device 3 and the determination device 4 of FIG.

The sampling value before and after the polarity of the sampling value is inverted (the magnitude relationship with the zero value) or when the magnitude relationship with the offset value is inverted is stored in the sampling value storage means 11 as a set.

The intersection calculating means 12 obtains the time of the intersection which intersects the time axis of the zero level or the offset level by connecting a set of sampling values stored in the sampling value storage means 11 with a straight line (virtual line). (Ie, determined by interpolation).

The cycle calculating means 13 calculates the cycle based on the intersection obtained by the intersection calculating means 12. Here, the cycle calculating means 13 preferably calculates a half cycle of the waveform from an adjacent intersection of a set of sampling values and the intersection of the time axis.

The frequency calculating means 14 includes a period calculating means 13
The frequency f is calculated based on the cycle T obtained by the above.

In the embodiment of the present invention, preferably, the frequency is determined every half cycle, so that the number of times of the determination is increased and the accuracy is increased. In addition, since the frequency determination is calculated for each half cycle, detection of a change in frequency can be performed faster than the calculation for each cycle.

The sampling waveform whose frequency is to be determined is
When it is composed of two types of relatively high frequency (high frequency) and relatively low frequency (low frequency), a half cycle calculating means 15 for calculating a half cycle of both high frequency and low frequency waveforms
A determination reference time calculating means 16 for calculating a time as a determination reference based on the obtained half cycle, and determining whether the sampling waveform is a high frequency or a low frequency based on the obtained determination reference time. And a comparing / determining unit 17 for performing the comparison.

In the present invention, (a) sampling values to be written into the storage means as a set of sampling values before and after the sign value of each of a plurality of signals having different frequencies or when the magnitude relationship with the offset value is inverted. (B) for each signal, an intersection calculation processing for finding an intersection of a line connecting a set of sampling values and a time axis of a zero value or an offset value stored in the storage means; (C) a half-period calculation process for calculating the time of each half-period of the signal sampled on the basis of the intersection obtained by the intersection calculation means, and (d) a time as a criterion based on the half-period. And (e) a comparison determination process for making a comparison determination based on the time obtained by the determination reference time calculation process. Process (e) is realized by executing a program on a computer that constitutes the frequency determining device. In the present invention, the present invention can be implemented by reading out the program from a recording medium storing the program by a computer and executing the program.

Further, in the present invention, when there is a signal waveform for determining that the signal waveform is composed of a low-frequency signal waveform, a high-frequency signal waveform, and a high-frequency and low-frequency waveform, The frequency and the half cycle of each of the low-frequency signals are defined as t1 and t2, and the time t2-t1 between the zero-cross points of the two waveforms with the time axis is determined.
And a reference point is defined on the time axis by taking the ratio of the frequencies of the low frequencies, the time to the reference point is defined as t ′, and the zero cross point t of the signal waveform to be determined with the time axis is t
When 1 ≦ t <t ′, the frequency is determined to be a high frequency, and t ′
When ≤t≤t2, a process for determining a low frequency is provided, and this process is realized by executing a program on a computer constituting the frequency determination device. In the present invention, the present invention can be implemented by reading out the program from a recording medium storing the program by a computer and executing the program.

[0030]

[Embodiment] An embodiment in which the present invention is applied to a specific example of the above embodiment will be described. FIG. 3 is a diagram for explaining a determination method according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a sampling waveform. With reference to FIG. 3, the calculation of the frequency in one embodiment of the present invention will be described.

In FIG. 3, the time axis t (the zero level of the amplitude, which is the horizontal axis), where the signal has an offset,
(Corresponding to the offset level), the sampling points sandwiching the zero-cross point are defined as (a, b), (c, d),
(E, f) (a <b <c <d <e <f).

Sampling points (time) a, b, c, d,
The sampling values (values on the vertical axis) at e and f are x1, x2, x3, x4, x5, and x6, respectively.

As shown in FIG. 3, the distances between the sampling point and the zero-cross point are α, β, γ, and δ. Let the sampling period be τ and the waveform periods be T1 and T2.

Here, when the values of α, β, γ, and δ are obtained,

Assuming that the number of continuously positive sampling values is n1, T1 / 2 = α + (n1-1) × τ + β (2)

Therefore, the period T1 to be obtained is: T1 / 2 = (x2 × τ) / (x2-x1) + (n1-1) × τ + (x3 × τ) / (x3−x4) T1 = 2τ ｛x2 / (x2-x1) + (n1-1) + x3 / (x3-x4)｝ (3)

Similarly, when the number of consecutive negative sampling values is n2, T2 / 2 = γ + (n2-1) × τ + δ (4)

T2 = 2τ {x4 / (x4-x3) + (n2-1) + x5 / (x5-x6)} (5)

As shown in FIG. 4, low frequency, high frequency,
It is assumed that there are three types of signal waveforms to be determined. The waveform for making this determination is composed of high-frequency and low-frequency waveforms. At this time, the ratio is calculated at the zero cross point of the low frequency and high frequency waveforms. Here, the high frequency is 2100 Hz (half cycle = t1), and the low frequency is 1300 Hz (half cycle = t2).

FIG. 5 is an enlarged view of a portion surrounded by a rectangle A in FIG. The point obtained by taking the ratio is used as a reference point for determination.

High frequency (2100Hz), low frequency (1300Hz)
Are defined as t1 and t2. Then, when the time between the zero-cross points of both waveforms is obtained, it becomes t2-t1.

Based on 2100 Hz and 1300 Hz, a reference point is determined in a ratio of 13:21. The time to the reference point is t '
Then, t ′ = t1 + 13/34 × (t2−t1) (6)

T1 = 1/2100/2 = 238.10 μsec, t2 = 1/1300/2 = 384.62 μsec

By substituting the obtained t1 and t2 into the above equation (6), t ′ = 294.12 μsec

When 238.10 ≦ t <294.12 (where t is a zero crossing point), the frequency of the signal to be determined is 2100 Hz
When 294.12 ≦ t ≦ 384.62, the frequency of the signal to be determined is determined to be 1300 Hz.

According to the frequency determination apparatus described as an embodiment of the present invention, the frequency determination of a signal sampled at a low sampling rate can be performed accurately and in a short time, and a small error can be determined. Frequency determination device 1
05.

[0047]

As described above, according to the present invention,
This has the effect of accurately determining the frequency of a signal sampled at a low sampling rate, which has been conventionally difficult.

Further, according to the present invention, there is an effect that a change in frequency can be detected quickly and with high accuracy.

The reason is that, in the present invention, the frequency is measured in a half cycle of the sampling frequency, and the frequency change is made faster in the half cycle than in the frequency judgment in each cycle. This is because detection can be performed, more frequency determination can be performed for a certain time period, and errors are reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a frequency determination circuit according to one embodiment of the present invention.

FIG. 2 is a diagram showing a flow of frequency determination according to one embodiment of the present invention.

FIG. 3 is a diagram for explaining one embodiment of the present invention;
The symbols necessary for performing frequency judgment are shown.

FIG. 4 is a diagram showing a sampling signal waveform for explaining one embodiment of the present invention.

FIG. 5 is a partially enlarged view of FIG. 4;

FIG. 6 is a diagram illustrating a system configuration of a wireless access network including a frequency determination device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sampling device 2 Memory 3 Computing device 4 Judgment device 11 Sampling value storage means 12 Intersection computing means 13 Period computing means 14 Frequency computing means 15 Domain engine computing means 16 Judgment reference time computing means 17 Comparison / judging means 101 Fixed telephone 102 Fixed station 102 Wireless access device) 103 Base station (wireless access device) 104 Time switch (TSW) 105 FSK signal frequency determination device 106 A / D converter 107 Switch 108 Two-wire telephone line (2-wire metallic wire) 109 Digital highway

Claims (9)

[Claims] A first step of storing, as a set, sampling values before and after a magnitude relationship between a sampling value of a sampled signal waveform and a sign value or an offset value is inverted in a storage means; A second step of finding an intersection where a stored straight line connecting a set of sampling values intersects a time axis of a zero value or an offset value; and sampling based on the intersection obtained in the second step. A third step of calculating a half cycle of the obtained signal, and a fourth step of calculating a frequency based on the half cycle derived in the third step. . 2. A method for determining a signal frequency including a high-frequency waveform and a low-frequency waveform, the method comprising: when a magnitude relationship between a sampling value and an offset value is inverted for each of a plurality of signals having different frequencies. A first step of storing in the storage means a set of sampling values before and after the above, and for each of the signals, stored in the storage means,
A second step of finding an intersection where a straight line connecting a set of sampled values and a time axis of a zero value or an offset value intersects; each of the signals sampled based on the intersection obtained in the second step A third step of calculating a half-period time; a fourth step of calculating a time to be a criterion based on the half-period obtained in the third step; and a fourth step of obtaining a time as a criterion. And a fifth step of comparing and judging the frequency of the signal to be judged based on the time used as the judgment criterion. 3. When there is a signal waveform for determining which is composed of a low-frequency signal waveform, a high-frequency signal waveform, and a high-frequency and low-frequency waveform, the high-frequency signal and the high-frequency signal Each half cycle of the low frequency signal is defined as t1 and t2, a time t2-t1 between the zero cross points of the two waveforms with respect to the time axis is obtained, and a ratio between the high frequency and the low frequency is calculated. A reference point is set on the axis, the time to the reference point is defined as t ′, and a zero-cross point t of the signal waveform to be determined with respect to the time axis.
When t1 ≦ t <t ′, the frequency of the signal waveform for performing the determination is determined to be a high frequency, and when t ′ ≦ t ≦ t2, the frequency of the signal waveform for performing the determination is determined to be a low frequency. 3. The frequency determination method according to claim 2, wherein: 4. A storage means for storing a set of sampling values before and after the magnitude relationship between the sampling value of the sampled signal waveform and the polarity of the sampling value or the offset value is reversed, and stored in the storage means. Intersection calculation means for finding an intersection where a straight line connecting a set of sampling values and a time axis of a zero value or an offset value intersects, and a half cycle of a signal sampled based on the intersection obtained by the intersection calculation means. A frequency judging device comprising: means for calculating; and means for calculating a frequency based on the derived half cycle. 5. An apparatus for determining a signal frequency including a high-frequency waveform and a low-frequency waveform, wherein when a magnitude relationship between a sampling value and an offset value is inverted for each of a plurality of signals having different frequencies. Storage means for storing the sampling values before and after as a set, and for each of the signals, stored in the storage means,
Intersection calculation means for finding an intersection where a straight line connecting a set of sampling values and a time axis of a zero value or an offset value intersects; each half cycle of a signal sampled based on the intersection obtained by the intersection calculation means A half-period calculating means for calculating the time, a half-cycle obtained by the half-period calculating means, a judgment reference time calculating means for obtaining a time to be a judgment reference, and a half-cycle obtained by the judgment reference time calculating means. Based on time,
A frequency determination device, comprising: comparison determination means for performing a comparison determination. 6. When there is a signal waveform for determining which is composed of a low-frequency signal waveform, a high-frequency signal waveform, and a high-frequency and low-frequency waveform, the high-frequency signal and the high-frequency signal Each half cycle of the low frequency signal is defined as t1 and t2, a time t2-t1 between the zero cross points of the two waveforms with respect to the time axis is obtained, and a ratio between the high frequency and the low frequency is calculated. A reference point is set on the axis, the time to the reference point is defined as t ′, and a zero-cross point t of the signal waveform to be determined with respect to the time axis.
When t1 ≦ t <t ′, the frequency of the signal waveform for performing the determination is determined to be a high frequency, and when t ′ ≦ t ≦ t2, the frequency of the signal waveform for performing the determination is determined to be a low frequency. The frequency judging device according to claim 5, wherein: 7. A frequency judging device according to claim 4, wherein the frequency judging device judges a frequency of a signal output from a time switch. 8. An apparatus for judging a signal frequency including a high-frequency waveform and a low-frequency waveform, comprising: (a) a magnitude relationship between a positive or negative sampling value or an offset value for each of a plurality of signals having different frequencies; (B) for each signal, a straight line connecting the set of sampled values, a zero value or an offset, stored in the storage means, for each signal; (C) calculating the time of each half cycle of the sampled signal based on the intersection obtained by the intersection calculation means; and (d) calculating the half time of the signal. A judgment reference time calculation process for obtaining a time as a judgment reference based on a cycle; and (e) a comparison judgment process for performing a comparison judgment based on the time obtained by the judgment reference time calculation process. , The (a) to a recording medium recording a program for executing on a computer that constitutes the frequency determining device processing (e). 9. The recording medium according to claim 8, wherein there is a signal waveform for making a judgment made up of a low-frequency signal waveform, a high-frequency signal waveform, and a high-frequency and low-frequency waveform. In this case, the half cycle of each of the high-frequency and low-frequency signals is defined as t1 and t2, and the time t2-t1 between the zero-cross points of the two waveforms with the time axis is obtained. The reference point is determined on the time axis by taking the ratio of the frequencies of the above, and the time to the reference point is defined as t ′, and the zero crossing point t of the signal waveform to be determined with the time axis is determined.
When t1 ≦ t <t ′, the frequency of the signal waveform to be determined is determined to be high frequency, and when t ′ ≦ t ≦ t2, the frequency of the signal waveform to be determined is determined to be low frequency And a recording medium for recording a program for executing the program on a computer constituting the frequency determination device.